Bores with sealed seating created by precision-grinding and formed by a bezel are found in fuel injection pumps for internal combustion machines, for example. A tappet is movably disposed in the bores and conveys the desired amounts of fuel. To be able to guide the tappet sealingly in the bore, the surface of the bore is honed. When a defined pressure has been reached, the conveyed amount of fuel is delivered via a valve, whose sealed seating is formed by the bezel at the inlet of the bore, and on which a so- called sealing needle is seated as the valve element.
Precision processing of the bore is provided by honing and precision processing of the bezel by precision-grinding. As a rule, the bezel is first made by means of a grinding tool and is subsequently precision-ground by means of a tool. In the process, the tool is guided in a cylindrical guide which is a part of the tool holding fixture. The disadvantage in this case is that it is not possible to remove the offset of the axis of the tool guide relative to the bore in the workpiece, in fact it is possibly even increased.
Internal grinding of valve seats by means of a grinding tool is known from German Published, Examined Patent Application DE-AS 10 52 262. The grinding tool is rotatably seated on a guide rod which is received in a bushing which, in turn, is inserted into a guide bore. The guide rod does not turn during processing. Accordingly, the grinding tool rotatably seated on the guide rod can be displaced in the vertical direction with respect to the guide rod. Many sources of errors regarding the concentricity of the bore and the bezel result from the seating of the guide rod in a bushing, the seating of the bushing in a second bushing and the vertically displaceable guidance of this second bushing with respect to a cylindrical body which bears the grinding disk.
Furthermore, in connection with a bore for fuel injection pumps whose sealed seating is to be worked on it is not acceptable to tightly insert a bushing into the bore and a guide rod into the bushing, since the bore can be damaged in the process. German Published, Examined Patent Application DE-AS 10 52 262 obviously relates to the production of valve seats for internal combustion engines. This is suggested in the reference by the cylindrical recess following the valve seat, which could be a portion of a gas guiding channel. In such a case it is not necessary that the valve shaft which is subsequently inserted into the guide bore be exactly guided, instead it is mainly used for the transmission of force to the valve disk.
U.S. Pat. No. 4,147,462 discloses an arrangement for precision-grinding of the valve seats in an engine block. In this case a guide rod is firmly wedged into the valve tappet bore. The conical cutting tool for working the valve seat is guided on this guide rod but is at the same time double-mounted on gimbals with respect to the drive spindle, as is the guide rod, so that it is possible to compensate for an error in alignment of the drive spindle and the engine block. Fixing the guide rod in such a way is not possible in connection with the previously mentioned type of processing because in this case the surface of the bore would be damaged in an unacceptable manner. In addition, the play between the guide rod and the conical cutting tool would represent a further source of inaccuracies in processing the bezel.
U.S. Pat. No. 2,978,846 discloses a diamond-studded drilling tool for materials which are difficult to work, which is embodied as a stepped tool. It has a drill tip, followed by a guide portion and adjoining this an enlarged drill area, so that it is possible to drill a bore and a bezel at the same time. Precision-working of the bezel while maintaining concentricity, however, cannot take place in this way. It would also have to be performed in a further process step.
A grinding tool for precision-working of conical valve seats or sealing faces and also of fuel injection nozzles is known from German Patent Publication DE 29 12 814 C2, wherein the spindle which supports the conical grinding tool for working the sealing face is seated in a bushing (spindle sleeve) around which the actual workpiece is eccentrically rotated. This guidance results in a one-sided and only linear contact between the workpiece and the spindle sleeve. Such seating is not sufficiently exact to meet the requirements of an extremely exact concentricity between bezel and bore. Furthermore, this processing principle cannot be applied to a sealing face tapering toward the bore and formed by a bezel at the inlet of a bore.